Integumentary System PDF

The Integumentary System A. Introduction 1. the integumentary system is an organ system composed of: a. the skin (cutaneous membrane) b. derivatives of the skin (i.e., accessory structures): i. hair & hair follicles ii. nails iii. sweat & sebaceous gl...

The Integumentary System A. Introduction 1. the integumentary system is an organ system composed of: a. the skin (cutaneous membrane) b. derivatives of the skin (i.e., accessory structures): i. hair & hair follicles ii. nails iii. sweat & sebaceous glands 2. functions of the integumentary system: a. protection –barriers are of 3 types i. physical ii. chemical iii. biological b. thermoregulation c. excretion d. cutaneous sensation e. vitamin D synthesis f. blood reservoir B. The Skin 1. skin is composed of two layers: a. epidermis – thinner, superficial portion of the skin b. dermis – lies deep to the epidermis 2. the hypodermis (superficial fascia or subcutaneous layer) lies deep to the dermis a. this layer is made up of areolar & adipose tissue b. the hypodermis anchors the skin to underlying organs  N1630/1310: The Integumentary System, pg 2 c. acts as a shock absorber and insulates the deeper body tissues d. contains the major blood vessels that supply the skin 3. the dermis – the deep layer of the skin a. composed of dense irregular CT containing mostly collagen fibers & smaller amounts of elastic and reticular fibers b. the dermis consists of 2 layers – reticular & papillary i. reticular layer 1) deeper & thicker layer (dense irregular CT) 2) lines of cleavage –formed by separations between collagen bundles within the tissue 3) tearing of fibers in this layer results in striae (stretch marks) ii. papillary layer 1) thin, superficial layer (areolar CT) 2) the upper surface is marked with projections called dermal papillae iii. anchor cells to basement membrane c. contains numerous blood vessels, nerve fibers, a variety of sensory receptors, the major portions of hair follicles, and sebaceous & sweat glands 4. the epidermis a. composed of keratinized stratified squamous epithelium organized into 4 or 5 distinct layers i. thick skin has 5 layers –located in high friction areas (palms & soles) ii. thin skin has 4 layers –covers remainder of body surface b. epidermis is avascular  N1630/1310: The Integumentary System, pg 3 c. epidermis contains several different types of cells – including: i. keratinocytes – the main type of cell in the epidermis 1) produce keratin 2) keratinocytes arise from the deepest layer of the epidermis ii. melanocytes 1) highly branched cells which produce melanin 2) located in deep layer of the epidermis 3) transfer melanin keratinocytes, which then accumulate the granules in superficial regions of their cytoplasm 4) there are 2 main types of melanin –both types are derived from the amino acid tyrosine a) most common form is brown-black in color b) other main form is pink-to-red in color c) both the amount and type of melanin produced is controlled by a number of genes expressed with incomplete dominance iii. Langerhans’ cells (aka epidermal dendritic cells) 1) a type of fixed macrophage located in deeper layers of epidermis 2) protect against bacterial invasion iv. Merkel cells (aka tactile cells) –specialized epithelial cells which serve as sensory receptors for touch d. the epidermal layers – from deep to superficial: i. stratum basale 1) consists of a single row of keratinocytes 2) many cells in this layer are highly mitotic stem cells  N1630/1310: The Integumentary System, pg 4 3) also present: melanocytes & Merkel cells ii. stratum spinosum 1) cells are only slightly mitotic, and there is no further mitosis beyond this layer 2) cytoskeleton of keratinocytes contains bundles of intermediate filaments a) called tonofilaments b) composed of pre-keratin 3) cells are somewhat flattened & irregularly shaped iii. stratum granulosum 1) relatively thin layer consisting of flattened cells which have begun to die due to lack of nutrients 2) “grainy” appearance of cells in this layer due to the presence of 2 types of cytoplasmic granules: a) keratohyalin granules –involved in formation of keratin b) lamellar granules –contain a glycolipid that, when secreted, helps to waterproof the superficial layers of the epidermis iv. stratum lucidum 1) only occurs in “thick skin” areas 2) cells in this layer are dead 3) in this layer, and also in the stratum corneum, tonofilaments are converted to keratin v. stratum corneum 1) outermost & thickest layer of the epidermis 2) contains 20-30 layers of shingle-like dead cell remnants completely filled with keratin 3) the cells of this layer are continuously shed – and continuously replaced by cells being pushed up from deeper layers  N1630/1310: The Integumentary System, pg 5 e. disruptions in skin homeostasis i. pressure injury (previously known as pressure ulcer, pressure wound or “bedsore”) may result from a loss of or restricted blood flow to the tissue ii. primary lesions iii. secondary lesions  The Tissues A. It all starts with fertilization 1. fertilization = fusion of a sperm and ovum, creates a zygote 2. typically occurs in the upper (i.e., initial) part of the uterine tube B. Formation of Primary Germ Layers & Embryonic Membranes 1. Stage 1: Cleavage a. this period of rapid mitotic cell division begins about 24 hr after fertilization b. blastomeres –identical cells formed by cleavage divisions c. morula –solid mass of blastomeres surrounded by zona pellucida, usually reaches uterus approx 4 days after fertilization 2. Stage 2: Blastocyst Stage a. blastocyst is a hollow ball which forms (via cells rearranging themselves) when the morula contains exactly 32-cells b. mitotic divisions continue i. by the end of the 5th day, the blastocyst is composed of 100s of cells ii. these cells are of 2 types: 1) trophoblast 2) inner cell mass or embryoblast  The Tissues, pg. 2 3. Stage 3: Implantation a. trophoblast cells secrete enzymes which break down the zona pellucida & allow blastocyst to “hatch” at end of day 4 b. blastocyst then floats free in uterine cavity until day 7-8, when it adheres to the endometrium (lining of the uterus) and embeds in uterine wall c. trophoblast cells form 2 distinct layers: i. cellular trophoblast (also called the cytotrophoblast) –inner layer ii. syncytial trophoblast (also called the syncytiotrophoblast) –outer layer d. implantation process takes approx 1 wk and is typically finished by day 14 e. human chorionic gonadotropin (hCG) i. begins to be secreted by trophoblast cells during implantation 1) later secreted by chorion 2) ultimately, placenta takes over this endocrine function ii. functionally similar to LH (luteinizing hormone) --helps to maintain uterine lining f. during implantation, the inner cell mass is also undergoing changes i. becomes a bilaminar embryonic disc –develops into the embryo proper ii. separation in the epiblast becomes the amniotic cavity, which fills with amniotic fluid  The Tissues, pg. 3 4. Stage 4: Gastrulation –i.e., formation of the primary germ layers a. this phase begins soon after amnion forms b. main events of the phase: i. embryonic disc elongates and the primitive streak appears on the dorsal surface ii. a third germ cell layer develops –bilaminar embryonic disc transforms into a three-layered embryo iii. the primary germ layers: 1) endoderm 2) ectoderm 3) mesoderm a) mesenchyme b) notochord iv. all the body organs derive from the primary germ layers 1) endoderm → the epithelial linings of the digestive, respiratory, & urogenital systems, and the glands associated with these systems 2) ectoderm → the structures of the nervous system and the skin epidermis 3) mesoderm → virtually everything else  The Tissues, pg. 4 C. Overview & Introduction to Tissues 1. terminology –important prefixes a. tissues = groups of similar cells which are specialized to perform a specific function b. histology = the study of tissues (hist- = tissue) 2. four major types of tissues & their general functions: a. epithelial (ET) b. connective (CT) c. muscle d. nervous 3. 3 general features help to anchor cells & stabilize tissues: a. glycoproteins on cell surface b. basement membranes c. intercellular junctions 4. the basic types of cellular junctions: a. tight junctions –result from fusing together of transmembrane proteins of adjacent cells b. adherens junctions i. dense protein layer at inner surface of plasma membrane (a plaque) attaches to membrane proteins & cytoskeletal proteins ii. transmembrane glycoproteins, called cadherins, attach intracellularly to a plaque –extend through plasma membrane & attach to cadherins from an adjacent cell iii. cadherins are one type of cellular adhesion molecule (CAM) iv. adhesion belts (areas of extensive adherens junctions) are often present in epithelial tissues  The Tissues, pg. 5 c. desmosomes i. similar to adherens junctions ii. additionally, have intermediate filaments attached to inner surface of plaque – extend through cytoplasm & attach to desmosome on opposite side of cell d. hemidesmosomes i. hemidesmosome plaque: 1) has transmembrane integrin proteins inserted 2) integrins attach to laminins on outside of cell 3) intermediate filaments attach to plaque on cytoplasmic face ii. anchor cells to basement membrane e. gap junctions i. adjacent cells are close together ii. there are fused transmembrane proteins in the plasma membrane which form hollow cylinders called connexons iii. connexons of adjacent cells connect in the intercellular spaces to form gap junctions iv. allows passage of chemical substances between cells D. Epithelial Tissues 1. special characteristics a. high degree of cellularity b. specialized cellular contacts  The Tissues, pg. 6 c. polarity i. ET always has one free surface (called the apical surface) which is exposed to the body exterior OR to the cavity of an internal organ (called the lumen) ii. saying that ET cells exhibit polarity, simply means that the cells near the apical surface are different than the ones nearer the basal surface d. avascularity -- ET contains no blood vessels e. presence of a basement membrane i. basement membrane consists of 2 layers of extracellular matrix: 1) basal lamina (aka lamina lucida) – thin layer secreted by the ET cells, acts as selective filter between the blood & the ET 2) reticular lamina (aka lamina densa)– deeper layer, made up of a fine network of collagen fibers produced by the underlying CT ii. basement membrane anchors & supports the ET f. avascular but has nerve supply g. high regenerative capability 2. covering & lining epithelium a. specific functions i. primary function is protection  The Tissues, pg. 7 ii. controls permeability – thus, helps regulate materials that enter/leave the body 1) absorption & secretion 2) filtration & excretion iii. surface transport iv. sensory functions b. classification: i. the various types of ET can be classified according to: 1) the number of cell layers present a) simple – single layer of cells b) stratified – two or more layers of cells c) pseudostratified – cells falsely appear to be stratified, but there is only one cell layer present 2) cell shape (classification is based on the height of the cells in the apical layer of the ET) a) squamous – thin & flattened b) cuboidal – cube-shaped c) columnar – long & narrow c. specific types of covering & lining epithelium i. simple epithelium 1) simple squamous –specific examples include: a) endothelium b) endocardium c) mesothelium  The Tissues, pg. 8 2) simple cuboidal 3) simple columnar a) may be either ciliated or non-ciliated b) goblet cells are present in both types 4) pseudostratified columnar ii. stratified epithelium 1) stratified squamous 2) stratified cuboidal 3) stratified columnar 4) transitional 3. glandular epithelium a. gland – consists of one or more ET cells specialized to produce and secrete a product called a secretion b. functionally, glands are classified as either/or: i. endocrine – secrete hormones directly into the interstitial fluid surrounding the secreting cell ii. exocrine 1) structurally, exocrine glands may be unicellular or multicellular a) unicellular –secrete onto the epithelial surface (i.e., a body surface) b) multicellular –secrete product into a duct that opens on an epithelial surface  The Tissues, pg. 9 2) functional classification of exocrine glands a) merocrine glands i) secrete by exocytosis -- cell isn’t damaged in any way by the secretory process ii) most common type of multicellular exocrine gland in body b) holocrine glands i) entire cell becomes laden with secretory products, then bursts ii) cell is destroyed by the secretory process c) apocrine glands i) accumulate secretory product in the apical region of the cell ii) pinch off part of the apical region in the secretory process D. Connective Tissue (CT) 1. overview a. CT is the most abundant tissue in the body b. various types: i. connective tissue proper ii. cartilage iii. bone iv. blood c. Why classify all these tissues as connective tissue? Two reasons: i. common embryonic origin –all arise from mesenchyme ii. role of extracellular matrix 2. general structure of CT a. composed of 2 basic components: extracellular matrix & cells  The Tissues, pg. 10 b. extracellular matrix is the nonliving component of CT – it consists of ground substance & fibers i. ground substance 1) unstructured material between the cells 2) consists of interstitial fluid (which is mostly water), CAMs, polysaccharides & proteoglycans 3) the types of proteoglycans & the relative amounts of them helps determine the properties of the matrix ii. fibers –three types: 1) collagen fibers 2) elastic fibers 3) reticular fibers c. cells –the living component of CT i. each major class of adult CT has a primary cell type that exists in the immature (-blast) and, in some cases, a mature (-cyte) forms ii. –blast stage 1) fibroblast 2) chondroblast 3) osteoblast 4) hemocytoblast –the hematopoietic stem cell iii. -cyte stage  The Tissues, pg. 11 iv. other cells are also present in CT --including 1) adipocytes 2) leukocytes (i.e., white blood cells) 3) mast cells 4) macrophages 3. CT types (and sub-categories) a. embryonic CT –the main type (and the only type we’ll worry about now) is mesenchyme b. connective tissue proper i. loose CT 1) areolar CT 2) adipose tissue 3) reticular CT ii. dense CT 1) dense regular CT 2) dense irregular CT 3) elastic CT c. cartilage i. overview 1) “chondro-”refers to cartilage  The Tissues, pg. 12 2) chondrocytes lie in pockets (called lacunae) within the matrix 3) matrix is gel-like in consistency and avascular 4) cartilage is surrounded by perichondrium, a dense irregular CT membrane, which is highly vascularized ii. the 3 types of cartilage 1) hyaline cartilage a) glossy, bluish-white in appearance b) matrix contains a firm ground substance and very fine collagenous fibers c) the most abundant type of cartilage in the body 2) fibrocartilage a) little ground substance b) matrix contains dense parallel masses of collagenous fibers in the matrix → very tough tissue 3) elastic cartilage a) similar to hyaline cartilage b) however, matrix contains more elastic fibers than hyaline cartilage d. bone i. the hardest connective tissue ii. 2 types of bone tissue 1) compact bone 2) spongy bone iii. organization of compact bone 1) basic unit is the osteon  The Tissues, pg. 13 2) main parts of the osteon: a) lamellae (layers of matrix material) form around the central canal b) osteocytes sit in lacunae, which lie between lamellae c) canaliculi project from lacunae iv. organization of spongy bone 1) matrix is arranged in irregular columns (trabeculae) 2) spaces between trabeculae are filled with red or yellow marrow d. blood i. blood is fluid CT ii. main components of blood: 1) cells –which derive from mesenchymal cells 2) plasma –which is the (fluid) matrix 4. fascia –the CT layers that surround & support body organs & structures a. superficial fascia –aka hypodermis or subcutaneous layer b. deep fascia c. subserous fascia  The Tissues, pg. 14 D. Muscle Tissue 1. consists of elongated cells, specialized to contract (shorten) and cause movement 2. contain the contractile proteins, actin & myosin Muscle Type Location Appearance Type of Nervous Control Skeletal attaches to & moves the striated voluntary bony skeleton Cardiac occurs only in the heart, striated involuntary where it contracts to pump blood through the heart & into the blood vessels Smooth (visceral) found in walls of smooth (non- involuntary internal organs, blood striated) vessels, respiratory passages, etc. E. Nervous Tissue 1. located only in the nervous system 2. consists of 2 general cell types: a. neurons– the branching cells which receive & transmit electrical impulses b. neuroglial cells –supporting cells F. Membranes 1. a membrane is a thin layer of tissue which covers a surface, lines a cavity, or divides a space or organ 2. two general types a. epithelial membranes –composed of an epithelial layer and an underlying CT layer b. synovial membranes –composed of CT only  The Tissues, pg. 15 3. types of epithelial membranes a. mucous membranes i. line cavities which open to the outside of the body (e.g., respiratory & digestive tracts) ii. composed of epithelium (may be simple or stratified) over a thicker layer of loose CT (called the lamina propria) b. serous membranes i. moist membranes that line body cavities that do not open to the outside, and that cover organs in that cavity ii. composed of simple squamous ET which lies on top of subserous fascia iii. serous membranes consist of 2 layers: 1) parietal layer lines body cavity 2) parietal layer reflects back over the organs in the cavity to form the visceral layer iv. serous fluid is secreted into the potential space between the visceral & parietal layers v. specific serosa you will be encountering 1) pleura 2) pericardium 3) peritoneum c. cutaneous membrane –usually referred to as “the skin” 4. synovial membranes –line joint cavities of freely moveable (synovial) joints  The Tissues, pg. 16 G. Maintaining Homeostasis: Wound Repair 1. wound repair involves 2 general types of events a. regeneration –replacement of damaged/destroyed tissue with an identical tissue b. fibrosis –proliferation of fibrous CT (scar tissue) 2. the general process of tissue repair a. Step 1: inflammation i. triggered by release of chemical mediators from local mast cells & damaged tissue cells ii. if bleeding has occurred, a blood clot forms –the part of the clot that is exposed to air forms a scab iii. tissue debris is removed from the area by phagocytes which have migrated there as a result of tissue damage b. Step 2: migratory and organization phase i. this phase begins during inflammation ii. begins with migration of cells from stratum basale into the epidermal area of injury –they proliferate, forming new epidermis iii. fibroblasts also migrate to the area –will regenerate damaged hypodermis/dermis and also produce scar tissue iv. blood clot is replaced by granulation tissue c. Step 3: proliferative phase i. tissues & blood vessels continue to regenerate ii. scab detaches, epithelium thickens d. Step 4: maturation phase i. scab is shed, epidermis is fully regenerated ii. fibroblasts decrease in number  Introduction to the Human Body A. Terminology 1. anatomy = study of body structure 2. physiology = study of body function 3. structure-function relationships a. structure determines function b. function modifies structure 4. understanding A&P is foundational for clinical practice –which is why integrating A&P and Physical Assessment make sense a. important “tools” used in physical assessment: i. inspection ii. palpation iii. percussion iv. auscultation b. sign = objective physical indication of disease c. symptom = a subjective indication of disease or a change in condition B. Organizational Levels 1. chemical –includes atoms & molecules  Introduction, pg 2 2. cellular –cells are the smallest living units of the body 3. tissues a. = groups of similar cells organized to perform a common function b. four basic types: epithelial, connective, muscle, nervous 4. organs -- complex groups of tissues organized to perform a specific function 5. organ system – groups of organs that work closely together to perform a common purpose 6. organism – the most complex level of organization, an individual living thing C. Characteristics of Life – we share them with all other living entities 1. maintenance of boundaries -- living organism has to keep internal environment distinct from external environment 2. responsiveness – the ability to respond to physical and chemical changes in the internal and external environment 3. growth & differentiation a. growth = the ability to increase in body size, without important changes in body shape b. differentiation = the process by which a cell becomes specialized to perform a specific function 4. metabolism & excretion a. metabolism = the sum of all the chemical reactions that take place in the cells (catabolism + anabolism) b. excretion = the removal of waste products from the body  Introduction, pg 3 5. movement – including moving body as a whole from one location to another, moving body parts, and/or moving materials around in the body 6. reproduction –occurs on two levels a. cellular reproduction -- in which original cell divides into 2 identical daughter cells b. organismic reproduction –results in new human organism D. Homeostasis 1. homeostasis = the maintenance of a stable internal environment (dynamic equilibrium) 2. involves the processes required to maintain internal conditions within the narrow limits that are tolerable and necessary for health and survival 3. homeostasis is maintained via 2 general mechanisms: a. intrinsic regulation (aka autoregulation) b. extrinsic regulation 4. control of homeostasis a. involves 3 interrelated elements (receptor, control center, effector), and the feedback mechanism(s) between those elements b. receptor = a sensor c. control center -- determines the tolerable range for the variable, analyzes input, and when necessary induces a response  Introduction, pg 4 d. effector e. feedback may be either/or: i. negative feedback –effector activity reverses/reduces original stimulus ii. positive feedback –effector activity enhances/intensifies the stimulus f. thermoregulation -- an example of negative feedback g. example(s) of positive feedback h. homeostatic imbalances i. disorder ii. disease